Of course it's agood improvement, just imagine that I just updated form a 5200 and I feel a huge difference with a 6600. Now, I think thatn the X700 is better than the 6600. Just think about it!
My pc only has pci in it so i can't upgrade until I finish my new rig. I bought a 6600 GT Turbo Charged Edition, so now all I need is the mobo and a good cpu, then I can worry about my spu later.